Climate change is helping “vectors” bring communicable diseases north

Malaria, West Nile, dengue – these are all diseases most associated with tropical countries. Yet with the change in global climate, diseases that once remained in the south, might be moving north.  In the April edition of The Canadian Communicable Disease Report, Nicholas Ogden, associate professor in the Département de Pathologie et Microbiologie (Department of Pathology and Microbiology) at the University of Montreal, explains that cases of malaria – and other infectious diseases – may be coming to Canada.

Diseases like malaria are known as vector-borne diseases, meaning they can be transmitted to humans via another living host. Malaria in particular is caused by the plasmodium parasite, but these parasites need to be delivered to a human by a “vector”. The typical malaria “vector” is the common mosquito. Other vector-borne diseases include lyme disease and the plague.

In the past, Canada has been kept safe from many of these diseases by our climate. Cold winters reduce tick, mosquito and flea populations, which in turn reduces the chances of populations of these vectors from contracting and propagating disease-causing parasites. However, since 1948, Northern Canada has been warming at a rate more than twice as fast as the global average. What this means for Canadians is increasingly hospitable climate for disease-carrying insects. But this is not the only reason Canadians have to be concerned about infectious diseases, Ogden warns.

Canadians’ Google search frequency for the term “Lyme Disease” since 2004, normalized by the highest number of searches over all time (ex. A value of “50” means half as many searches occurred at this time compared to the maximum number of searches)

An aging population like Canada’s is much more at risk since the body’s immune system and speed of recovery becomes worse. Additionally, a public health system that simply is not prepared for these tropical diseases could make their spread particularly dangerous. When asked if Canada’s health system is ready to combat infectious (potentially “exotic”) mosquito-borne diseases, Nurse Anne-Marie Lanctôt, manager of community health services at Concordia University, says that the Canadian healthcare system may be better prepared than other healthcare systems.  However, the key caveat Nurse Lancôt mentions is that other healthcare systems, especially the ones where mosquito-borne diseases are endemic, may have more experience dealing with outbreaks and epidemics – our own healthcare system may result in some initial “scrambling” before we get on our feet to deal with an epidemic of dengue.

The Canadian Communicable Disease Report warns that climate change could increase the prevalence of food-borne illnesses as well. The report explains, “Climate and climate change may directly impact infectious disease emergence and re-emergence via effects on pathogen survival, arthropod vector survival and reproduction, contamination of water and, in the case of zoonoses [diseases caused by microbes], abundance of reservoir hosts (the animals that harbour the microbes).” 

While climate change rhetoric often revolves around rising ocean levels, melting ice caps, and animal extinction, the Canada Communicable Disease report emphasizes that Canadians, too, stand to be affected, and that “identifying these risks is a key activity to assessing our vulnerability as a nation, and a starting point to identifying where public health effort is required to reduce the vulnerability and exposure of the Canadian population.”

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